[iOS]UIVisualEffectView(高斯模糊)中遇到的valueForUndefinedKey:类型的crash解析

前情提要

在iOS8版本的系统以后，需要实现高斯模糊的效果，通常我们的实现方法是如下代码实现的

    #define OS_VERSION_8_LATER  ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0)
    if (OS_VERSION_8_LATER) {
        UIBlurEffect *blur = [UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];
        _visualView = [[UIVisualEffectView alloc] initWithEffect:blur];
    }

---

遇到的问题

�系统类型的crash信息log

参考如下问题:

• SVProgressHUD Crash
• 在iOS8下的NSUnknownKeyException

---

解决问题

为了防止程序在出现意外的NSUnknownKeyException类型的crashlog信息，可以使用oc特有的kvc特性和runtime机制进行解决

思路
通过转移特定类型，例如CALayer的valueForUndefinedKey:和setValue:forUndefinedKey:的实现过程
实现方案

• 添加NSObject类型的类目NSObject+VFUK类目
• 在类目文件NSObject+VFUK.h中添加+ (void)addCustomValueForUndefinedKeyImplementation: (IMP)handler;
• 添加实现过程

+ (void)addCustomValueForUndefinedKeyImplementation: (IMP)handler
{
    Class clazz = self;
    
    if (clazz == nil)
        return;
    
    if (clazz == [NSObject class] || clazz == [NSManagedObject class])
    {
        NSLog(@"不要为%@类添加自定义的valueForUndefinedKey:或setValue:forUndefinedKey:方法", NSStringFromClass(clazz));
        return;
    }
    
    SEL vfuk = @selector(valueForUndefinedKey:);
    SEL svfuk = @selector(setValue:forUndefinedKey:);

    @synchronized([NSObject class])
    {
        Method nsoMethod = class_getInstanceMethod([NSObject class], vfuk);
        Method nsmoMethod = class_getInstanceMethod([NSManagedObject class], vfuk);
        Method origMethod = class_getInstanceMethod(clazz, vfuk);
        
        Method set_nsoMethod = class_getInstanceMethod([NSObject class], svfuk);
        Method set_nsmoMethod = class_getInstanceMethod([NSManagedObject class], svfuk);
        Method set_origMethod = class_getInstanceMethod(clazz, svfuk);
        
        
        if (set_origMethod != set_nsoMethod && set_origMethod != set_nsmoMethod)
        {
            NSLog(@"%@已经自定义过%@名字的方法实现.",NSStringFromClass(clazz), NSStringFromSelector(svfuk));
            return;
        }
        if (origMethod != nsoMethod && origMethod != nsmoMethod)
        {
            NSLog(@"%@已经自定义过%@名字的方法实现.",NSStringFromClass(clazz), NSStringFromSelector(vfuk));
            return;
        }
        
        if(!class_addMethod(clazz, svfuk, handler, method_getTypeEncoding(set_nsmoMethod)))
        {
            NSLog(@"为%@类添加%@方法失败", NSStringFromClass(clazz),NSStringFromSelector(svfuk));
        }
        
        if(!class_addMethod(clazz, vfuk, handler, method_getTypeEncoding(nsoMethod)))
        {
            NSLog(@"为%@类添加%@方法失败", NSStringFromClass(clazz),NSStringFromSelector(vfuk));
        }
    }
}

---

测试代码

• AppDelegate.m

static id UnknownExceptionKeyIMP(id self, SEL cmd, NSString* inKey)
{
    NSLog(@"exception key:%@,class:%@", inKey, [self class]);
    return nil;
}

@implementation AppDelegate

+ (void)initialize
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        [NSArray addCustomValueForUndefinedKeyImplementation: (IMP)UnknownExceptionKeyIMP];
        [NSString addCustomValueForUndefinedKeyImplementation: (IMP)UnknownExceptionKeyIMP];
    });
}
@end

• ViewController.m

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    NSArray *array = @[@"1",@"2"];
    
    [array setValue:@"xiaohao" forKey:@"name"];
    
    NSLog(@"%@",[array valueForKey:@"name"]);

    NSLog(@"可以相应该方法:%d",[@"xiaohao" respondsToSelector:@selector(name)]);
}

---

输出结果

exception key:xiaohao,class:__NSCFConstantString
exception key:xiaohao,class:__NSCFConstantString
exception key:name,class:__NSCFConstantString
exception key:name,class:__NSCFConstantString
(
    "",
    ""
)
可以相应该方法:0

由此，我们便可以针对性的解决由于系统sdk原因导致的莫名NSUnknownException

还是希望大家bug少少的.